This invention relates to a method of providing multi-channel telephony services and to signal processing apparatus for a multi-channel telephony system.
A variety of services may be required by telephone calls such as speech recognition, dual tone multi-frequency (DTMF) tone detection, voice playback and recording, and facsimile transmission and reception. These services may be provided through digital processing.
U.S. Pat. No. 5,497,373 issued Mar. 5, 1996 to Hulen describes a multimedia interface for a multi-channel telephony system. The interface comprises a central processing unit (CPU), shared memory, and a plurality of digital signal processors (DSPs). The shared memory stores signal processing programs used in providing services, such as voice recognition. A host messaging center downloads a service map for the telephone channels to the shared memory as a service table. The CPU identifies services required for each channel from this service table and, for each different required service, identifies a DSP to perform the service and downloads a program for processing the service from shared memory to the identified DSP's on-chip memory. In this way, one signal processing program may be stored in each DSP so that each DSP may process the required service for a number of telephone channels. Thus, where, for example, a telephone channel requires the services of voice messaging and dual tone multifrequency (DTMF) tone recognition, one DSP will be downloaded with a program to provide voice messaging signal processing and another DSP will be downloaded with a program to provide DTMF tone recognition signal processing. Further, each of these two DSPs will provide these services to other channels requiring these services.
A drawback with this approach is that if all of the DSPs are engaged in signal processing, a new service cannot be provided for a channel without overwriting a signal processing program in a DSP. This impacts other channels for which the DSP had been providing signal processing. To reduce the likelihood of this occurring, the number of DSPs may be increased, however, this increases the cost of the multi-media interface.
This invention seeks to overcome drawbacks of prior multi-channel signal processing apparatus.